Injury to the anterior cruciate ligament (ACL) results in a threat to an active lifestyle and exposes the patient to risk of early osteoarthritis. ACL reconstruction is typically chosen by individuals to allow a return to their previous work and sports activities. The results of primary ACL reconstruction have in general been good at restoring functional stability, but patients' long-term outcome remains unknown. The Multicenter Orthopaedic Outcomes Network (MOON) is an established consortium designed to enroll and longitudinally follow a multicenter cohort of ACL reconstructed patients to determine the modifiable predictors (or risk factors) of long-term outcomes of ACL reconstruction in order to establish patient-specific predictive models of clinically important outcomes. The objective of this prospective multicenter cohort of ACL reconstructions is to identify both the long-term prognosis and the potentially modifiable predictors of symptoms of osteoarthritis (OA), sports function, activity and general health through validated patient- reported outcomes, and incidence of ACL reconstruction graft and/or contralateral ACL failures. Our previous grants (R01 AR053684) have allowed us to enroll 3,547 patients and obtain both 2 and 6 year follow-up on this cohort. At both time points, we have been able to obtain a minimum of 84% follow-up using validated patient-reported outcome questionnaires and 93% via phone follow-up. In addition, a nested cohort or 317 ACL reconstructed patients returned onsite after 2 years for a comprehensive clinical assessment, specialized radiologic measurements, along with completing their patient-reported outcomes. The objective of this grant is to longitudinally follow these two cohorts at 10 years utilizing the same validated outcome measurements as well as following incidence of clinical graft and/or contralateral ACL failure. Further, nested cohort will help determine the predictors of and the correlates from clinical assessment with both the symptoms and signs of OA and validated outcomes (in terms of sports function, activity, and general health). This grant focuses on the predictors for ACL reconstruction outcome at 10 year follow-up, and will be accomplished by three Specific Aims. Aim 1 will identify the risk factors or predictors of return to sports function, physical activity level, and patient-reported quality of lfe. Specific Aim 2 will identify those risk factors or predictors measured at the time of the ACL reconstruction associated with symptoms of early osteoarthritis at 10 years post-surgery. Specific Aim 3 will identify incidence of additional surgery and graft failure performed on patient following ACL reconstruction. Once the risk factors or predictors for worse outcomes are identified, surgeons can be educated in potential modifiable variables to improve the outcome.